TNF and inflammatory bowel disease: [27] Other studies on IBD consistent with these findings led the authors to hypothesize a negative effect of insufficient levels of vitamin D on the retention rate of anti-TNF drugs [35], as well as to highlight the association between low vitamin D levels before anti-TNF therapy and reduction of achievement of remission after three months of treatment [36] or to presume that levels of vitamin D could be associated with disease activity and that the supplementation of vitamin D could increase the serum concentration of infliximab [19,20,21,22,23,24,25].